JPH011221A - Method for manufacturing polarizable electrodes - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an electric double layer capacitor and a secondary battery.

The present invention relates to a method for manufacturing polarizable electrodes used in electrochromic displays and the like.

BACKGROUND ART The first condition for activated carbon as a polarizable electrode used in electric double layer capacitors and the like is that it has a large specific surface area. For this purpose, activated carbon powder made by steam-activating sawdust and activated carbon fiber made by carbonizing phenol resin fibers have been used. Most of these activations occur at high temperatures of 8oO to 1600℃, resulting in the release of water vapor and CO.
21 hydrocarbons etc. are used as the activating gas.

Furthermore, in order to efficiently extract the electric double layer capacity accumulated on the surface of activated carbon, a technique has also been developed in which an Al current collecting layer is formed by plasma spraying. FIG. 3 is a cross-sectional structural diagram of an example of such an electric double layer capacitor,
Polarizable electrode 100 made of activated carbon fiber. Al collector electrode 1o1. formed by plasma spraying on this. Separator 102 consists of metal cases 103, 104 and gasket ring 105. The polarizable electrode 1oo and the separator 102 are impregnated with an electrolytic solution in which tetraethylammonium verchlorate is dissolved in propylene carbonate.

Problems to be Solved by the Invention Conventionally, in order to obtain activated carbon, as mentioned above, 8oo~
Oxidizing gas containing oxygen such as H2O was reacted with carbon powder and carbon fibers at a high temperature of 1500 tl. The reaction at this time is shown in Formula 1.

High temperature Cn+H20-m-C,, 10 Cot+H2↑・(1) In other words, at high temperature, oxygen atoms in water vapor gas react with carbon and themselves become co and H2 gas, and carbon becomes Cn-1. Activated carbon with a specific surface area of 1000 to 2500 m'/9 was obtained by forming fine pores on the surface and making it porous. By the way, it is obvious that on the surface of the activated carbon thus obtained, in addition to carbon atoms, oxygen atoms exist in the form of carboxy groups, phenolic hydroxyl groups, lactone groups, etc., as shown in Figure 4. There was no such thing. This amount is a very small value as the concentration of acidic functional groups is less than 1 mmole per y of carbon, but when this is used as a polarizable electrode such as an electric double layer capacitor, this site will react with the electrolyte. They could become active sites and promote the decomposition of the electrolyte.

Therefore, the presence of such acidic functional groups is not desirable in terms of improving leakage current and withstand voltage of the capacitor.

Furthermore, in the solid-gas reaction at high temperatures as described above, there is a limit to how much the carbon surface can become highly porous due to the progression of Equation 1.
It depends on the starting material, but the specific surface area is 2700rr? /f was the limit. Since the capacitance of the capacitor is directly proportional to the specific surface area of the activated carbon, it is desirable to further increase the capacitance in order to increase the capacitance of the capacitor.

Means for Solving the Problems In order to solve such conventional problems, the present invention provides a polarizable material characterized in that the surface of carbon or activated carbon is activated by ion beam irradiation or plasma sputtering. The present invention relates to a method for manufacturing an electrode.

Effects According to the present invention, it is possible to obtain activated carbon which has a very low surface oxygen concentration and a higher specific surface area than conventional activated carbon, and which improves the capacitance, internal resistance, and Characteristics such as leakage current can be greatly improved.

Embodiments Before describing specific embodiments of the present invention, the basic contents of the present invention will be explained with reference to the drawings.

FIG. 1 is an example of an apparatus for activating carbon used in the present invention. Rotary pump 1. In a reaction chamber 3 evacuated by a diffusion pump 2, a conductive electrode 4 for placing a sample for processing and an anode 6 face each other. The degree of vacuum in the reaction chamber is 1o-2 due to the Ar gas introduced from the gas introduction hole 6.
~10-'torr is maintained, and Ar plasma 9 is generated in the Pel jar by the matching box 7 and the RF power source 8. The processed sample 1o is exposed to this Ar plasma 9. 11.12 is cooling water. At this time, the carbon surface is struck by the accelerated Ar+jC, and surface carbon atoms are ejected from the carbon substrate due to the exchange of flight energy of the atoms, creating holes in this area and making the carbon porous. This process is equivalent to using carbon as a sputtering target material. In this figure, RF2
The method of glow discharge type high frequency sputtering is shown.
DC sputtering.

The carbon material may be exposed to plasma such as by magnetron RF sputtering. Further, an accelerated ion beam (for example, an Ar"4 on beam) may be collided with the carbon substrate 15. FIG. Ar ion 1
6 collides and surface carbon atoms 17 are released from the substrate 15,
A hole is formed here, and as this hole is repeated, the surface of the base body 16 becomes porous. The carbon substrate 16 used at this time may be carbon or activated carbon obtained by a conventional steam activation method. Particularly in the latter case, the removal of acidic functional groups on the surface also occurs simultaneously with the formation of porosity.

Next, specific examples of the present invention will be described.

(Example-1) Carbonized phenolic resin fiber (diameter 107a.

Woven fabric (carbon content 95%) (basis weight 14oy/'r
r? ) is processed by the apparatus shown in FIG. The treatment time was 30 minutes, and an aluminum layer with a thickness of 100/1 m was formed on one side of the treated fabric by plasma spraying. Using a separator electrolyte (propylene carbonate solution of tetraethylammonium verchlorate 1 mol/l), a capacitor shown in FIG. 1 is prototyped. The diameter of the electrode is 6 circles.

(Example-2) Activated carbonized phenolic resin fiber (diameter 1Q 74m
, Carbon content 94%, specific surface area 2000rr? /
9) Example 1
The same capacitor as in Example 1 was produced as a prototype by processing in the same manner as in Example 1.

(Comparative Example-1) In Example-1, carbon fibers not subjected to the treatment of the present invention are used for electrodes.

(Comparative Example-2) In Example-2, activated carbon fibers not subjected to the treatment of the present invention are used for electrodes.

The characteristics of the above capacitor are shown in the table.

In this embodiment, only Ar sputtering is shown, but the same effect can be obtained by using an ion beam method, and gases such as oxygen, ammonia, and CF4 are suitable as the gas used. When oxygen is used, the carbon surface is slightly oxidized and the effect of reducing functional groups cannot be obtained, but a high specific surface area can be achieved.

Any of powder, plate, sintered body, graphite, and amorphous carbon can be used as the carbon substrate.

Although we have described electric double layer capacitors as an example of using carbon materials, the present invention can also be greatly applied to polarizable electrodes for secondary batteries and electrocomic displays.

Effects of the Invention According to the present invention, since carbon is activated in a reduced pressure atmosphere such as a plasma atmosphere or ion beam irradiation, a completely new activated carbon different from that obtained by the conventional high-temperature steam activation method can be obtained. It is possible to greatly improve the characteristics of the capacitor used.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the carbon substrate processing apparatus used in the present invention, Fig. 2 is a schematic diagram showing the principle of the processing of the present invention, and Fig. 3 is a cross section of a coin-shaped capacitor using activated carbon fiber polarizable electrodes. The structural diagram, FIG. 4, is a diagram schematically showing the surface functional groups of carbon. 1... Rotary pump, 2... Diffusion pump, 3... Reaction chamber, 4... Electrode,
6...Anode, 6...Gas inlet, 7.
... Switching box, 8 ... RF main power supply 9 ... Ar plasma, 10 ... Processing sample.

Claims (5)

[Claims] (1) A method for producing a polarizable electrode, which comprises activating the surface of carbon or activated carbon by ion beam irradiation or plasma sputtering. (2) The method for producing a polarizable electrode according to claim 1, wherein the carbon or activated carbon has the shape of a plate, sheet, fiber, or porous molded body. (3) The method for manufacturing a polarizable electrode according to claim 1, wherein the ion beam irradiation or plasma sputtering is performed in an inert gas such as nitrogen or Ar. (4) The method for manufacturing a polarizable electrode according to claim 1, wherein the ion beam irradiation or plasma sputtering is performed in an active gas such as oxygen, ammonia, or CF_4. (5) After activation, Al, T
2. The method for manufacturing a polarizable electrode according to claim 1, wherein any one of i, Nb, Hf, Zr, and Ta is formed on the surface of carbon or activated carbon.